Method of color control of ceramic products



2 sheets-sheet 1 J. Mcm. cpoLEY HETHOD 0E' lCOLOR CONTROL OF CERAMIC PRODUCTS Filed 0G12. 3, 1339 April 8 1941.

INVENTR. j. WM 605.627

, ATTORNEY.

April 8, 1941 J. Mcm. cooLEY 2.2371478 IETHOD 0F' COLOR CONTROL 0F CERAMIC PRCDUCTS Filed Oct. 3, 1939 2- Sheets-Sheet 2 INVENTOR.

ATTORNEY.

fatented Apr. 8, 1941 METHOD F COLOR CONTRUL 0F CERAMIC PRODUCTS John McManigal Cooley, East Palestine, Ohio, as-

signor to National Fircproofing Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Application October 3, 1939, Serial No. 297,674

2 Claims.

This invention relates to new and useful improvements in the firing of clay articles such as facing masonry for buildings or the like and more particularly to a method of cooling such articles in the kiln whereby the color of the article is controlled.

It is a primary object of the invention to provide a method of cooling kiln-fired clay products in a manner to positively control the color finish of such articles irrespective of atmospheric or other conditions which would influence the coloring of the material if left to a natural cooling rate. An essential feature of the invention is that the method of cooling controls the color finish without damage or injury to the product.

The invention deals particularly with a cooling process for salt glaze articles which will become more apparent from a description of the accompanying drawings constituting a part hereof in which like reference characters designate like parts and in which:

Fig. 1 is a diagrammatic View of a kiln employed in carrying out the method of this invention;

Fig. 2 a vertical cross-sectional view of the kiln taken along the lines 2-2, Fig. 1;

Fig. 3 a partial vertical cross-sectional View of the kiln stack and back-draft blower mechanism.

Withreference to the several figures of the drawings the structure therein illustrated comprises a kiln generally designated by the reference numeral I having a floor or hearth 2', a roof structure or crown 3 provided with one or more crown openings 4 having covers or closures 5 thereon, the kiln shown being of circular form having a sidewall 6 with angularly spaced fire boxes generally designated by the reference numeral l. The process may be adapted to rectangular kilns with equal success. The iire boxes are provided with openings 8 and are adapted to be lired by coal gaseous or liquid fuels. The re box chambers are provided with baffle walls 9 to prevent direct iiring of the product which is supported on the hearth 2.

The hearth or kiln floor 2 is provided with a plurality of waste gas exits IU which, as shown in Fig. l and Fig. 2 are of graduated sizes to obtain a uniform distribution of the products of combustion leaving the kiln chamber during the firing period or cooling air entering the kiln chamber in reverse direction during the cooling period, the openings ID communicating with exhaust passages II leading to a common exhaust passage I2 communicating with a stack I3. The passage I2 is controlled by a gate I4 and a vertical passage I is provided adjacent the stack for supplying cooling air to the kiln by the use of a fan or blower I6 for the purpose hereinafter explained.

In carrying out the method of this invention, it is desirable to have the blower i6 removable and replaced by a cover such as a steel plate during the ring of the clay products.

In the operation of the above described kiln for salt glaze clay products, the articles to be treated have been subjected to the usual preliminary drying to rid them of mechanical water and are ready for placing or setting on the kiln iioor. The product is essentially spaced on the kiln floor to provide circulating passages for the heating environment, and the treating fumes as well as the cooling air applied at different stages as hereinafter described.

When the kiln has been fully charged 'through openings or doors in the sidewalls7 not shown, the doors are closed in the usual manner by refractory brick or otherwise and the fire boxes are then Iired with the crown openings 4 closed, the stack draft damper I4 open, the blower removed and opening i5 closed.

The initial application of heat is slow and at relatively low temperatures to release the mechanical and hygroscopic water. The temperature is then gradually increased to burn out the combustibles and to oxidize any minerals contained in the clay product. This step also roasts-out any sulphur present. The preliminary and burning steps are slow to avoid generating steam in the product and also to prevent sealing of the surface thereof.

The next step in the firing operation is to increase the temperature at a faster rate during the vitricaton period at which stage the kiln is subjected to the iinishing temperature. This firing step is much faster than the initial step and after the product has attained the desired degree of vitrication, sodium chloride or common table salt is charged in the fire box into the re box chambers wherein it volatilizes and forms sodium chloride vapor, which ltrates through the entire kiln chamber, resulting in a chemical reaction with the surface of the product being fired, forming a soda alumina silica glass. The amount of salt charged at successive intervals into the fire box chambers determines the thickness of the glassy coating formed on the masonry facing materials and the sodium chloride vapors in the kiln are substantially uniformly distributed throughout the kiln in contact with the product` by means of the graduated waste gas passages Il] at the bottom of the kiln chamber, the rate of withdrawal of the sodium chloride vapors being controlled by the stack damper I4.

If after the salt vapor treatment the kiln were left to natural cooling through the stack draft,

and crown openings, the coloring of the product would vary in accordance with the stack draft and prevailing atmospheric conditions, such as a change in humidity, etc. Rapid cooling is necessary to secure desirable light shades of product demanded by the trade. When rapid rates of cooling are secured by natural stack draft or by opening doors or crown covers the product is damaged by air checking which occurs when cold air enters in direct contact with the product.

In accordance with the present invention, the cooling of the product is controlled to obtain a positive control of the coloring of the product without damage. Within the limitations of the deep coloring produced by too slow cooling and air checking, resulting from too rapid cooling, care must be exercised when subjecting the kiln to a forced cooling condition, which, in accordance with the present invention, is accomplished as follows:

After the last round of salt has been applied ,1,

to the kiln and the kiln atmosphere is fairly clear of sodium chloride fumes, firing is discontinued and the stack draft damper Ill which has been partially lowered during salting is raised to give the kiln the draft of the stack and the combustion air openings of the fire boxes are opened wide to exhaust the kiln chamber of all fumes. The kiln is allowed to cool in this manner for a short period, At this point the gate I4 of the stack passage I2 is closed entirely and the blower or u opened. The back draft thus produced causes a rapid temperature drop sufficient to produce the desirable light shades of salt glaze. The cooling air before entering the kiln chamber has been tempered during the passage through the hot stack flue I5 and the kiln bottom. This tempering of the cooling air prevents air checking and d-amage to the product and is the essential feature of the invention. The required rate of cooling will vary with kilns of different size and type of construction. In accordance with the present invention, the rate of cooling can be varied as required for the particular clay being processed or to suit the individual kiln being cooled. Control of the rate of the cooling is secured by change of volume of air admitted to the blower fan, a damper being provided for this purpose; also by control of the crown openings and nre box openings through which the air escapes from the kiln during the cooling period.

When the kiln is cooled to below 600 F. the back draft cooling may be discontinued. The back draft fan IE is removed and replaced by a steel or refractory plate and the gate I4 is raised toI induce a natural draft from the kiln to the stack. The kiln is allowed to cool naturally from this point on. The time and rate of cooling may be varied to obtain different color effects but cooling should be secured by the back draft method which may be done with positive control of rate of cooling without damage to the product.

It will be apparent from the foregoing description of the invention that the method provides positive control of the color finish of the product v by controlling the intensity and rate of cooling and by effecting a uniform distribution of the tempered cooling medium throughout the kiln chamber irrespective of atmospheric conditions.

Although one embodiment of the invention has lbeen herein illustrated and described it will be obvious to those skilled in the art that various modifications may be made in the details of construction Without departing from the principles herein set forth.

I claim:

, l. The method of applying a salt glaze to masonry facing materials which comprises placing said materials on the floor of the kiln in spaced relation to expose the surface of the material to the atmosphere of the kiln, subjecting the articles to a ring temperature to a degree of desired vitrication, then charging the kiln atmosphere with sodium chloride vapor to form a soda alumina silica glass surface on said material, exhausting the sodium chloride vapor from the kiln chamber by natural draft after firing has been discontinued, introducing cooling air into the kiln chamber through the stack flue and kiln bottom at a proper rate to lower the temperature of the articles so that the desired colors will be produced.

2. The method of applying a salt glaze to masonry facing materials which comprises placing said materials on the floor of the kiln in spaced relation to expose the surface of the material to the atmosphere of the kiln, subjecting the articles to a ring temperature to a degree of desired vitrincation, then charging the kiln atmosphere with sodium chloride vapor to form a soda alumina silica glass surface on said material, exhausting sodium chloride vapor from the kiln chamber, reversing the natural draft in the kiln by removing the crown covers and combustion chamber air openings, then shutting off the stack draft and subjecting the kiln chamber to a back draft by introducing air through the hearth of said chamber at uniformly spaced intervals on the door of the kiln, the degree and intensity of the back draft being such as to effect cooling of the kiln charge at a rapid rate until the charge has reached a temperature of 600 F. and then subjecting the charge to a natural stack draft and rate of cooling.

J. MCM. COOLEY. 

